Keyer circuit



Aug. 2, 1949. LOWE 2,477,634

Filed July 16, 1943 0 BSUPPLY B a K I E DONALD M. LOWE Patented Aug. 2, 1949 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 5 Claims.

This invention relates to a means for producing a sequential series of energy pulses and more particularly to a means for keying a normally blocked oscillator to produce a discontinuous train of oscillations.

There are, as well known by those skilled in the art, numerous methods of obtaining a discontinuous train of oscillations for use, for example, in radio echo ranging equipment. These include a wide variety of grid, plate, and cathode keying circuits. The present invention, however, pertains to a grid keying means synchronized with a given timing wave. Keying circuits of this class as provided by the prior art experienced such dimculties as low oscillator efiiciency incident to the comparatively long transition period of the oscillator in passing from the quiescent state to a state of oscillation. This disadvantage is more or less due to the gradual slope in the leading edge of the keying pulse which permits useless plate current to flow for a considerable period of time prior to the initiation of oscillations, thereby resulting in a low :efficiency of scillator operation.

It is therefore an object of this invention to provide a reliable, efficient grid keying circuit.

It is another object of this invention to provide a sequential series of impulses having a steep rising wave front characteristic.

It is another object of this invention to provide a suitable grid keying means for producing a discontinuous train of oscillations synchronized by a given timing wave.

Other objects and features of the present invention will become apparent upon a careful consideration of the following description when taken together with the accompanying drawings the figures of which are designed for the express purpose of illustration and not as a definition of the limits of the invention. Reference for the latter purpose is to be had to the appended claims.

Fig. 1 is :a schematic diagram of a preferred embodiment of the present invention and Fig. 2 is a series of voltage curves all having the same time axis and are drawn to represent the voltage wave forms at various points along the circuit contained in Fig. 1.

It is contemplated by the present invention to provide a means for producing a discontinuous train of oscillations and more particularly to produce a. series of "impulses having steep rising wave fronts from a given timing wave.

Reference is had more particularly to Fig. 1 wherein there is shown a preferred embodiment of the present invention, comprising triode l0 which is excited by a source of alternating voltage, say cycles for example, coupled to the control grid l2 by way of transformer H and through resistance IS the purpose of which will be pointed out hereinafter. The anode I6 of triode H3 is connected to the positive terminal of the high voltage supply, by way of the plate resistor l 4 and lead 15, which in turn is grounded, while the cathode H is connected to the negative terminal of the high voltage supply by way of lead l8 thereby throwing the cathode below ground. The output of triode H3 is resistancecapacitance coupled to the vacuum tube is by way of the difierentiating circuit comprising capacitance 20 and resistance 2!. Tube 19 is normally biased to cut-off by way of the self biasing circuit comprising resistance 22 and shunt capacitance 23 and also by the connection of resistance 24 from the cathode 25 to the positive side of the high voltage supply or ground. The output of tube 48 is fed through the primary winding of the coupling transformer 25 which is damped by way of resistance 2! in order to reduce transient responses to a minimum. This transformer is preferably of the step-up variety, the output of which appears across the secondary win-ding which is also damped by way of resistance 28 and connected across the grid cathode circuit of the vacuum tube 29, which tube is also normally maintained in a blocked condition. This tube is biased to cut-off by virtue of the voltage drop across resistance 39 connected to the cathode 3i and serially connected with the resistances 32 and 33 across the high voltage supply. The output of tube 29 is taken from the cathode 3| and fed through resistance 36 to the grids of a tuned grid, tuned cathode oscillator, for example, not shown here.

The theory of operation of the present invem tion is as follows: Let it be assumed, for example, that a sixty cycle sine wave voltage is being fed into the input transformer II which is preferably of the step-up type. Thus the positive half cycle input to triode It drives the tube beyond saturation while the negative half cycle drives the tube beyond cut-off. During the positive half cycle the grid I2 is drawing considerable current to produce an IR drop across resistance 13 thereby squaring the actual positive half cycle of input voltage to resemble that shown by the solid Curve A in Fig. 2. Thus the output from tube H] is substantially a square wave similar to that of Curve B of Fig. 2. The square wave output of tube 40 is differentiated by the coupling circuit comprising capacitor 20 and resistance 2| to produce a pair of opposite polarity spaced apart pulses as shown in Curve C which represents the actual input to vacuum tube l9. Since tube I9 is normally biased to cut-off negative inputs do not effect the flow of plate current but positive inputs initiate a surge of plate current through the primary winding of the coupling transformer 26 to produce a voltage impulse across the primary thereof similar to that shown in Curve D. The resistance 21 prevents the primary winding from ringing when kicked by the surge of plate current and consequently eliminates any transient oscillations. The input pulse across the primary winding is inverted. in phase as shown in Curve E and applied across the grid cathode circuit of the normally blocked vacuum tube 29. Thus tube 29 is rendered conducting to effectively shunt resistance 32 and 33 with the now low impedance of the tube thereby causing a large surge of plate current from tube 29 to flow through resistance 30 and produce a voltage drop across this resistance in accordance with the input voltage pulse as shown by the solid line Curve F. At the same time condenser 35 which is eifectively in series with resistance 36 across the high voltage supply and which is normally maintained in a charged condition is discharged through tube 29 in response to the input pulse applied thereto. Thereafter condenser 35 is recharged through resistance 30. The action of the circuit is such as to produce a voltage output pulse across resistance 30 similar to that illustrated by the dotted line in Curve F.

It therefore becomes apparent that a suitable steep wave front keying pulse may be obtained from the cathode of tube 29 or in effect across the resistance 30 which is applied to the grids of the oscillator, not shown here, through the resistance 34. This keying pulse abruptly drives the oscillator into oscillation thereby causing the grids to draw current to charge condenser 36 negative to quench oscillations and thereby produce an oscillation pulse equal in time length to the charging time of condenser 36. Thus after oscillations have been quenched condenser 36 begins an exponential discharge through resistance 34 to maintain the oscillator in a quiescent state until the occurrence of the next keying pulse. It therefore becomes obvious that the regulation of resistance 34 must be such as to prevent double pulsing, that is, to prevent condenser 36 from discharging until the keying pulse has terminated and also must be such as to discharge condenser 36 before the occurrence of the next keying pulse. The changes in oscillator grid voltage are more adequately shown in Curve G of Fig. 2. The sharp rise in grid voltage corresponds to the leading edge of the keying pulse (dotted Curve F), while the sharp drop in grid voltage occurs during the charging of condenser 36 during the period of oscillations and the exponential decay occurs with the discharge of condenser 36 through resistance 34.

Turning again to the keying pulse as shown by the dotted Curve F. It is obviously desirable to have a steep rising wave front on the leading edge in order to abruptly drive the tube from the blocked or quiescent state into oscillation thereby maintaining to a minimum the interval of time during which the tube is drawing useless current. It is also desirable to have a sloping trailing edge in order to maintain the oscillator in a state of oscillations long enough to charge condenser 36 and thereby self-quench the oscillations.

In the past there has been some difiiculty experienced with the grids of pulse oscillators becoming contaminated and thereby emitting electrons which results in a rapid discharge of condenser 36, for example, before the termination of the keying pulse to cause double pulsing. The applicant avoids this problem by operating the grids of the oscillator at a considerable below ground potential so that keying of the oscillator can be accomplished by a below ground pulse.

In summarizing, the following advantages are contained in the present invention: High oscillator efiiciency due to the steep rising wave front in the keying pulse as mentioned heretofore. Closer coupling of the load to the oscillator with a corresponding increase in output, which is apparently due to the rapid rise in plate current to a value for which the mutual conductance is sufiiciently high for oscillations to start readily. Synchronization is made much more positive since there is a comparatively rapid termination of the keying pulse which allows a wide adjustment of resistance 34 without double pulsing.

Although I have shown and described only a certain and specific embodiment of the present invention, I am fully aware of the many modifications possible thereof. Therefore this invention is not to be restricted except insofar as is necessitated by the prior art and the spirit of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A keying circuit comprising a source of high voltage, a voltage divider network connected across and including at least two resistance elements, a condenser connected in shunt with one of said resistance elements, a normally nonconducting vacuum tube connected in shunt with said one of said resistance elements, output means connected across the other of said resistance elements, and means operative to render said vacuum tube momentarily conductive whereby an output pulse is formed at said output means having an abrupt leading edge and a sloping trailing edge.

2. A keying circuit comprising a source of high voltage, a voltage divider network connected thereacross and including at least two impedance elements, a condenser connected in shunt with one of said elements, a normally non-conducting vacuum tube connected in parallel with said one of said impedance elements, an output means connected across the other impedance element of said divider network, and impulse generating means operative to render said vacuum tube momentarily conductive whereby an output pulse is formed at said output means having an abrupt leading edge and a sloping trailing edge.

3. In combination, an oscillator circuit including at least one electron discharge device having a control electrode therefor, a keyer circuit for said oscillator comprising a source of high voltage having positive and negative terminals, said positive terminal being connected to ground potential, a voltage divider network connected across said high voltage supply and including a condenser shunting a portion of said network, low resistance means operative to momentarily shunt said shunted portion of said divider network whereby an output pulse is formed across the unshunted portion of said divider network, and means including a parallel connection of resistance and capacitance connecting said control electrode to the junction of said shunted and unshunted portions of said voltage divider network.

4. In combination, an oscillator circuit including at least one electron discharge device having a control electrode therefor, a keyer circuit for said oscillator comprising a source of high voltage having positive and negative terminals, said positive terminal being connected to ground potential, a voltage divider network connected across said high voltage source and including at least two impedance elements, a condenser connected in shunt with one of said impedance elements, a low resistance means operative to momentarily shunt said one of said impedance elements whereby an output pulse is formed across the other of said impedance elements having an abrupt leading edge and a sloping trailing edge, and means including a parallel connection of resistance and capacitance connecting said control electrode to the junction of said one impedance element and said other impedance element oi. said voltage divider network.

5. In combination, an oscillator circuit including at least one electron discharge device having a control electrode therefor, a key circuit for said oscillator comprising a source of high voltage having a positive terminal and a negative terminal, said positive terminal being connected to ground, a voltage divider network connected across said source of high voltage and including at least two impedance elements, a condenser connected in shunt with one of said impedance elements, a normally non-conducting electron discharge device connected in shunt with said one of said impedance elements, means operative to render said non-conducting discharge device momentarily conductive whereby an output pulse is formed across the other of said impedance elements having an abrupt leading edge and a sloping trailing edge, and means including a parallel connection of resistance and capacitance connecting said control electrode to the junction of said one of said impedance elements and said other of said impedance elements.

DONALD M. LOWE.

REFERENCES CITED The following references are of record in the file of this patent:

-- UNITED STATES PATENTS Number Name Date 1,933,219 Nakajima Oct, 31, 1933 2,097,066 Hoover Oct. 26, 1937 2,166,688 Kell July 18, 1939 2,181,568 Kotowski Nov. 28, 1939 2,407,272 Hart Sept. 10, 1946 FOREIGN PATENTS Number Country Date 482,724 Great Britain Apr. 4, 1938 490,622 Great Britain Aug. 18, 1938 

